Project Summary Alport syndrome (AS) is characterized by a triad of renal failure, sensorineural deafness, and ocular abnormalities in humans. This disease primarily affects males through an X-link mutation that results in the absence of novel, type IV collagen ?3.?4.?5 chains in the kidney GBM and in cochlear basement membranes (BMs). We propose to examine cochlear BM and the extracellular matrix (ECM) in X-linked mutant male mice that lack the ability to produce the ?5 type IV chains using immunohistochemistry, by serial sectioning with a light-sheet microscope (sTSLIM), and after decellularization to visualize large portions of the BM and the ECM by sTSLIM and SEM and immunolabeling of BM components with nanogold particles. We will also determine if functional changes in hearing occurs in mutant animals as determined by ABR and DPOAE hearing threshold testing. Further, we will determine if mutant animals are more susceptible to a moderate noise exposure than control animals and whether the mutation alone or noise exposure leads to a zone of separation at the BM between cells of the scala media and the underlying basilar membrane, similar to that observed in human cochleas from patients with AS. We expect to demonstrate replacement of the novel, type IV collagen chains (?3.?4.?5) in the BM of the basilar membrane by the more ubiquitous ?1.?.?2 collagen chains. We expect to observe hearing loss in the mutant mice either before or after a moderate sound exposure. We expect to observe lifting of the cells off of the basilar membrane of these animals and infiltration of cells into the spaces of Nuel in the organ of Corti in the mutant animals. Accomplishment of the goals of this proposal will determine the site and possible mechanism of hearing loss in mutant mice due to AS. If all of these observations are confirmed, then this model will serve a good animal model for the human disease. This information and animal model will be useful for developing therapies to prevent and minimize hearing loss in humans with AS. This is important since renal function in AS can be corrected by dialysis and transplantation; whereas, there is no therapy for hearing loss other than hearing aids.